1. Field of the Invention
This invention relates to optoelectronic package structures, and more particularly to structures which efficiently locate optical fibers in desired positions therein.
2. Description of Related Art
An optoelectronic package has to perform many functions. Many planar optoelectronic devices must be precisely aligned to other optical or optoelectronic components including optical fibers. The package must provide mechanical support to maintain required alignment permanently or at least for a designed end of life period. The devices dissipate an amount of heat which must be removed efficiently. Optical fibers need to be routed in and out of the package. Electrical inter-connections need to be provided, and in most cases the package has to be sealed hermetically. Thus package design is a critical issue in successful performance of such devices. A good package design will provide the above functionality in an efficient manner, but it will also ensure successful processing hierarchy, so that the process steps are sequential.
U.S. Pat. No. 6,227,724 by Verdiell for xe2x80x9cMethod for Constructing an Optoelectronic Assemblyxe2x80x9d describes an OptoElectronic (OE) module a flexible element referred to as a xe2x80x9cflexurexe2x80x9d which is bonded to an optical fiber, and used to align the fiber-core to a lens and a laser beam from a light-emitting device such as a laser. Alignment is performed prior to the sealing of the OE module with a separate lid. Process and alignment tooling are described for fixing the fiber in the flexure. After alignment the fiber is permanently attached to the flexure by soldering, brazing or welding. The flexure is secured to the substrate by spot welding with a laser or using UV curable adhesives to a substrate frame and to the substrate base, thereby reducing flexibility of the optical fiber since the flexure is attached to the substrate. In summary, the flexure is used to align and retain the fiber in position prior to sealing the cap hermetically.
U.S. Pat. No. 6,220,765 and divisional application U.S. patent application Publication Ser. No. 2001/0001622 A1 of Tatoh for xe2x80x9cHermetically Sealed Optical-Semiconductor Container and Optical-Semiconductor Modulexe2x80x9d discloses the fabrication of a sandwiched base plate laminated onto the bottom of an optical package solely to prevent warping that produces distortion of the optical signal transmitted through the optical window in a hermetic package. Two plates, each made of a material with a specific Young""s modulus are laminated together to produce a structure that will not warp during the package operation temperatures. While this may be relevant to Transmitting Optical Sub Assemblies (TOSAs) and Receiving Optical Sub Assemblies (ROSAs), it less relevant to the Wave Guide Package Structure (WGPS) of this invention where in one of the plates there is a very high conductivity material that allows spreading of local hot spots on a device.
U.S. Pat. No. 6,315,465 B1 of Mizue et al. for xe2x80x9cOptical Modulexe2x80x9d discloses a Lead Frame Base structure which is selectively etched or stamped and subsequently used to laminate additional wiring layers to accommodate the packages circuitry. The selective interconnectivity between layers in achieved by using both conductive and non-conductive epoxies. The sole purpose of this type of circuitry is to minimize the use of wire bonding as an interconnection technique that allows for tighter/shallower encapsulation which together minimizes inductance and impedance issues, yielding better electrical performance. The LED is supported and mounted externally of the encapsulated body by bending the two support leads. This has distortion issues when the temperature rises during operation. In any event, while Mizue et al. may have particular relevance in Optical Transmitter/Receiver packages it is of less relevance to the wave guide of this invention.
U.S. Pat. No. 6,270,263 B1 of Iwase et al. for xe2x80x9cOptical Modulexe2x80x9d describes and optical module with a silicon (Si) substrate mounted with optical devices (laser and photo diodes) and with wiring pattern on it. The substrate assembly is assembled with two synthetic resin pieces (top and bottom) sealed with an adhesive. The synthetic resin package has features such as various holes and ferules in configurations which allow for optical fiber(s) to be introduced into an assembled package and to be sealed next to the laser diode by an adhesive. A synthetic resin package material which is sealed with an adhesive is consider to be non-hermetic.
U.S. Pat. No. 5,355,429 of Lee et al. for xe2x80x9cOptical Fiber Strain Relief Apparatusxe2x80x9d discloses apparatus for reducing optical fiber strain in a limonite structure with strain relief hardware. The hardware can consist of anchor with crimp ring and connector adapter in various configurations. In an embodiment in which the fiber is bent at an angle the emphasis is upon protection of the optical fiber from external forces which are absorbed by the anchor and protective cabling, but there is no suggestion of providing slack in the optical fiber to accommodate strain due to Coefficient of Thermal Expansion (CTE) mismatch. Moreover, there is no discussion of strain relief in optoelectronic modules or packages.
U.S. Pat. No. 6,075,914 of Yeandle for xe2x80x9cApparatus for Connecting an Optical Fiber to an Optical Devicexe2x80x9d discloses a method of attaching a optical fiber in a xe2x80x98Vxe2x80x99 groove on a device without securing the fiber with an adhesive or solder. The securing of the fiber is on a inclined pad with adhesive away from the device which allows elastic deformation and urges the fiber into the xe2x80x98Vxe2x80x99 groove, but there is no discussion of packaging thereof.
U.S. patent application Publication Ser. No. 2001/0017964 A1 of Setoguchi for xe2x80x9cOptical Interconnection Modulexe2x80x9d describes a base formed of a high CTE material (as well as alumina). The base includes internal metallurgy, grooves for fiber alignment, multiple fiber alignment, matched index adhesives between the fiber and the laser, but there is no mention of any method for proving strain relief for the fibers nor is their any statement or concern about CTE strain in the fiber induced by the substrate during thermal excursions.
U.S. Pat. No. 6,273,620 B1 of Kato et al. for xe2x80x9cSemiconductor Light Emitting Modulexe2x80x9d is specifically related to a fiber grating laser module where the grating is formed within the fiber and hence the oscillation length can be adjusted independent of the Semiconductor Optical Amplifier (SOA). The drawings for the module incorporated in the patent do not show features related to an optical fiber strain relief structure.
U.S. Pat. No. 6,205,264 B1 by Jin et al xe2x80x9cOptical Assembly with Improved Dimensional Stabilityxe2x80x9d describes a process of incorporation of fine dispersoid particles in various solder compositions and a resulting structure provided for improvement in the creep properties of the solders thus giving a more dimensionally stable optical assembly created using these xe2x80x98improvedxe2x80x99 solders. There is no mention of a strain relief for optical fibers.
An object of this invention is to provide strain-relief in optical fibers connected to an optoelectronic package.
In accordance with this invention, an S-bend is provided in an optical fiber for strain-relief. The strain-relief S-bend is incorporated in the fiber to reduce stress on the optical fiber during thermal excursion of the package during operation of the devices contained therein and under various environmental conditions.
Further in accordance with this invention, the package includes retractable structures secured to the lid of the package. When the lid is placed in position to close the package the retractable elements are aligned with an existing fixed fiber-array which has sufficient slack to be deflected to form an S-bend without damage. The retractable structures push the optical fibers down into the package to produce strain relief S-bends in the optical fibers during the sealing of the lid of the package. The retractable structures are secured to the lid of the package. The retractable structures are composed of a material which can be retracted after use by shrinking thereof. For example, the retractable structures may be composed of porous glass or porous metal formed by powder metallurgy which can be shrunk by application of heat with a laser beam, a local hot wire above the cover or the like. Alternatively, the retractable structures can be composed of a low melting point material such as a gold-tin alloy which melts at about 280xc2x0 C. and coalesces into a globule spaced well away from the optical fiber.
In accordance with another aspect of this invention, an optical-electronic package, comprises at least one active device selected from the group consisting of electronic and optoelectronic devices with electrical connections from the active device and optical fiber connections from the active device. The package is formed by a high thermal conductivity base, a casing and a lid which are and hermetically sealed together. The base has a pedestal to support and provide heat transfer connection to the active device. A casing comprising sidewalls is bonded to the base. The package has passageways for the electrical connections from the active device and passageways for the optical fiber connections from the active device. The lid, which is hermetically sealed on top of the casing, has retractable means for forming a bend in the optical fibers to provide strain relief when the lid is placed on the casing. The retractable means which form a bend in the optical fibers are retractable once the lid is sealed onto the casing.
Preferably, the pedestal and base have internal electrical connections and contact pads on the surface of the pedestal and base for active device attach or wire bond and the retractable means is formed of porous material.
Preferably, the retractable means is formed of a retractable material which adapted to be withdrawn to retracted position when heated with a focused source of radiation and the retractable material is selected from the group consisting of a porous material and a low melting point alloy which coalesces into a globule in response to application of heat thereto.
Preferably the package includes fiber supports extending from the sidewalls thereof, preferably having grooved recesses therein.
Preferably, interconnection lines are formed through the casing to the device and/or interconnection lines are formed through the base to the device.
Preferably, the base is formed of a high thermal conductivity ceramic material and interconnection lines are formed through the base to the device, and/or the base is a high conductivity structure with internal wiring and pads on the surface of the top surface of the pedestal.
In still another aspect of the invention an optical-electronic package, comprises an electronic device formed on an ancillary element selected from the group consisting of a semiconductor chip or substrate; electrical connections from the ancillary element; optical fiber connections from the ancillary element; a high thermal conductivity base, the base having a pedestal to support and provide heat transfer connection to the ancillary element; and a seal band bonded to the base. A casing is bonded to the seal band by means selected from the group consisting of soldering and brazing providing a hermetic seal thereto. The casing has side feedthroughs for the electrical connections from the ancillary element, and the package having top feedthroughs or grooves for the optical fiber connections from the ancillary element. A lid is hermetically sealed on top of the casing, the lid having retractable means for forming a bend in the optical fibers to provide strain relief when the lid is placed on the casing, the retractable means for forming a bend in the optical fibers being retractable by thermal or mechanical means once the lid is sealed on the casing.
No flexible element is used to align a fiber-array to active or passive optical devices mounted on a raised platform (wave guides or VCSELs (Vertical-Cavity Surface-emitting Lasers).
The use of a lid with internal stepped features allows for controlled fiber bending during the hermetic sealing operation. The stepped features are subsequently retracted with a secondary heating step allowing for the free xe2x80x9cstress relievedxe2x80x9d movement of the fiber during operation.
The present invention provides a solution for device (waveguide based on other) mounted onto a thermally conductive substrate (aluminum nitride (AlN) silicon carbide (SiC) or other) which is hermetically sealed with solder, and a cover (metal) lid.